Nutrient flows and their influence on the cultivation of the edible mushroom Agaricus bisporus

Fungi, a vital kingdom within the Eukaryota domain, include diverse organisms such as molds, yeasts, and mushrooms, characterized by their unique cell walls made of glucan and chitin. Notably, the oldest filamentous fungus is estimated to be 2.4 billion years old, underscoring the evolutionary resilience of fungi, which thrive in various environments, including soils, oceans, and high-salt systems. In agricultural contexts, fungi play a critical role, particularly through the cultivation of edible mushrooms, which are recognized for their sustainability, nutritional and medicinal value. The global production of mushrooms and truffles surged significantly, particularly between 1961 and 2017. Key cultivable genera known as the “high five” include Agaricus (button and portobello mushrooms), Pleurotus (oyster mushrooms), Lentinula (shiitake), Auricularia (jelly ear), and Flammulina (enokitake). The economic impact of the edible mushroom industry is substantial, with an estimated worth of about $42 billion, and Agaricus alone accounting for 30% of global production. The cultivation of mushrooms, particularly the button mushroom, Agaricus bisporus, involves a complex, multi-phase process that begins with composting. This process transforms agricultural waste into a nutrient-rich substrate, which is essential for mushroom growth. The cultivation phases include fermentation, pasteurization, inoculation with spawns, and fruiting body formation. Factors influencing mushroom yield include compost composition, microbial interactions, and environmental conditions such as temperature, humidity, and CO2 levels. Additionally, the presence of beneficial microorganisms in the compost enhances yield by providing essential nutrients and suppressing pathogens. The aim of this doctoral thesis was to address gaps in understanding the interactions between A. bisporus and its compost ecosystem, particularly regarding nutrient dynamics. It explored how stable isotopes could elucidate nutrient transport and the role of microbial interactions in the compost food web. The research aimed to contribute to a more comprehensive understanding of the cultivation of A. bisporus and the ecological roles that the compost microbiome plays in the growth and development of the its mycelium and mushrooms. Overall, this study significantly enhanced the understanding of carbon and nitrogen transport within the mycelium and compost of Agaricus bisporus, highlighting a preference for using the top compost layer. It provided valuable insights into the compost microbial community dynamics, revealing complex interactions between A. bisporus and its microbial environment that impact bacterial biomass and growth. Moreover, the research showed A. bisporus's reliance on the microbial population for growth, with reduced activity in autoclaved compost. Additionally, the study confirmed that nematodes in compost, although present, do not threaten A. bisporus cultivation. Despite these findings, limitations were acknowledged, including the focus on A. bisporus, controlled laboratory conditions, and the use of simple tracers. Future research should address these limitations to better understand the interactions, potentially using advanced modeling techniques for comprehensive insights.